1. Field of the Invention
The invention relates to a method for automatically sorting objects and combining objects to assortments.
2. Description of the Related Art
In known sorting methods, the objects are gripped by controllable manipulation devices and placed into trays which are transported on a belt conveyor. Each gripped object is assigned to an assortment by the manipulation device wherein the position of this assortment is determined by the control of the manipulation device. Frequently, the number of objects to be combined to an assortment or the individual weight of the objects or the total weight of an assortment are used as sorting criteria.
The prior art reference WO 99/28057 describes a method for the automated grouping of objects. The objects are placed in random order in a continuous flow onto the belt conveyor and are subsequently moved into the predetermined sorting positions by manipulation devices. The sorting positions in this known method are provided on the belt surface of the belt conveyor transporting the objects wherein a detection device arranged upstream of the manipulation devices detects the random position and orientation of the objects and submits this information to a control unit. Depending on the determined order state, the control device then determines sorting positions and controls the manipulation robot based on the sorting positions such that the robot operates with a sorting efficiency as great as possible.
In known sorting devices, a manipulation device is provided as a placing device for each object type. It picks the objects that are assigned to it and places them into a corresponding sorting position. When sorting several object types into assortments, it is therefore required to have several processing stations which in the known method usually cooperate with one another in a processing line. The manipulation devices operate in a fixed interlinked way because of the required sorting output. The automated manipulation devices of the known sorting devices are therefore fixedly configured for certain sorting tasks, and a variation of the sorting tasks can be realized only with difficulty. Retrofitting or retooling the device for changing the sorting task often entails adding a further manipulation device which leads to high costs. Moreover, in the case of sorting devices which comprise several cooperating manipulation devices, it is not always possible to achieve the maximum overall device efficiency by means of the known method for automated sorting of objects because of the required interlinking of the manipulation device which necessitates synchronization of the sorting speed of all manipulation devices. Therefore, these manipulation devices or robots must operate at a minimal speed even though, in principle, they could fulfill the assigned sorting tasks more quickly but for reasons of synchronization of the entire device they must wait for slower working robots.
It is an object of the present invention to provide a method for automated sorting of objects which makes possible a faster sorting action for variable selection of different sorting specifications.
In accordance with the present invention, this is achieved in that the objects to be sorted according to a selected sorting specification are removed from a supply and placed onto a belt conveyor and are continuously conveyed into the working area of controllable manipulation devices which are used as placing devices, where they are gripped by a placing device and are positioned in a predetermined sorting position, correlated with the respective object and determined according to the sorting specification by means of a control unit. Each object is fed onto the belt conveyer in an intermediate position close to the predetermined sorting position by a manipulation device used as a feeding device and arranged upstream of the placing device.
Each feeding device first places the objects removed from the supply in a first position onto the belt conveyor, for example, near the receiving tray. This first position, after the transport of the objects into the working area of the placing device, is close to the desired object sorting positions so that the working distances of the placing devices are short. Accordingly, the placing device can perform additional working steps at high working speed. The efficiency of the feeding devices is optimized when the objects are fed onto the belt conveyor in an arrangement similar to the group arrangement in the supply. In this connection, the feeding devices remove the objects from the supply in the form of object groups. For example, for an order state of the objects in the supply in the form of layers with a matrix arrangement, respectively, the feeding devices can remove from the supply object rows of the matrix or parts of the rows of the matrix and place them onto the belt conveyor. The objects of the supply are thus individualized during feeding onto the belt conveyor and can then be moved quickly by the placing device from their easily accessible intermediate position on the belt conveyor into the sorting positions.
When sorting several object types and when producing assortments with preselected numbers of different objects, expediently those objects of an object type having a correspondingly higher number of objects in the assortment as prescribed by the sorting specification are placed closer to the object sorting position onto the belt conveyor than the objects of the other object type(s). In this way, the robots for manipulating the object types to be handled more frequently have shorter working distances, and this results in a correspondingly higher overall speed.
Advantageously, the objects are placed onto the belt conveyor in tracks of identical object types extending in the conveying direction. The object sorting positions can be allocated approximately parallel to the objects on the belt conveyor. For sorting the objects into containers, the containers are placed in random positions continuously onto the belt, and the objects of the object type with the greatest number of objects to be sorted per container are placed directly adjacent to the container. The distances between the object groups of objects removed simultaneously from the supply and placed simultaneously onto the belt are advantageously uniform so that a periodically repeated placement pattern results corresponding to the preselected number of objects per assortment and the number of objects placed simultaneously onto the belt conveyor. The distances are selected by the control unit by taking into account the number of objects to be placed simultaneously, i.e., according to the original order state of the objects in the supply, such that the placing devices can operate with maximum possible movement speed. The control unit adjusts all feeding devices and the placing devices arranged downstream by taking into account their respective manipulation efficiencies.
The method according to the invention makes possible the disconnection of the rigid interlinking of several sorting robots in a processing line as well as the linking of the placing devices to a certain object type so that the overall efficiency of the sorting process is increased and is not limited by the individual efficiency of the manipulation device which operates the slowest. The objects can be placed in a quick feeding step simply in a formation similar to that in the supply onto the belt conveyor wherein the placement in a pattern determined by the group spacings makes possible an easy coordination of the working cycles of the placing devices. The placement pattern is determined by the control unit of the sorting device as a function of the preselected sorting specification with consideration of the respective efficiency or handling capacity of the employed manipulation devices and, correspondingly, the optimal transport speed of the belt conveyor is adjusted.
In the two-step sorting method the placing devices and the feeding devices, which are connected to one another by the belt conveyor, can be spatially separated from one another. In this way, an efficient sorting device can be installed as a modular unit in any available space.
In the two-step sorting system with feeding devices and placing devices the placement pattern is determined as a function of the preselected sorting specification such that the movement courses of the employed placing devices are optimized. When it is determined that the efficiency of a placing device is not sufficient in order to sort all concerned objects of a particular type in the case of high numbers of objects per assortment, a less utilized placing device is switched online for filling the gap. Each placing device can manipulate any of the objects to be sorted. Expediently, the placement pattern and the control of the manipulation devices is adjusted such that the placing devices are used as uniformly as possible for sorting processes which require higher sorting efficiency and for sorting processes which require less sorting efficiency.
In a preferred embodiment of the invention, by means of a detecting device, for example, a camera arrangement, arranged between the feeding devices and the placing devices, the actual position of the objects on the belt conveyor is determined and the gripping movements of the placing devices for the individual objects are corrected. In this way, slipping of individual objects during feeding onto the belt conveyor can be taken into consideration and these objects can be moved without delay in the sorting process into the predetermined assortments. Also, defective products can be detected and can be excluded from the sorting process, for example, in the case of sorting of baked goods where broken pieces are eliminated.
High efficiencies of the total arrangement can be achieved when for the determination of the placement pattern the smallest common multiple of the respective number of objects of an object type per assortment and the number of these objects for each group being fed onto the belt conveyor are calculated. Based on these values, which relate to the respective object type, the control unit determines subsequently the smallest common multiple as a number of the assortments of the placement pattern, wherein, based on this number of assortments, the total number of respective object types to be supplied for each repetition of the placement pattern is determined. Expediently, the belt distance required for this placement pattern is compared with the available working area of the placing devices. When the control unit determines that the required belt distance exceeds the available working area of the placing device, for example, in the case of high numbers of objects of an object type in comparison to the numbers of other object types to be sorted, a multi-row placement of these objects onto the belt in the object track that has been determined as too long leads to a shortening of the belt distance.
A further optimization of the sorting efficiency is achieved when the group spacings of the object groups of a placement pattern, determined for the operation of the placing devices, are adjusted to the nearest approximated value which can be achieved with the efficiency of the feeding devices, and an adjusted placement pattern can be determined by means of the thus corrected group spacings. This adjustment of the placement pattern can be realized based on the above described calculation by means of a common multiple of the factors involved. When several placement patterns with different spacings are possible, the control unit determines the maximum achievable sorting efficiency by variation of the possible placement pattern, the belt speed of the belt conveyor, the variation of the tray spacings relative to one another, and the number of the employed manipulation devices. In this connection, the placing devices can be combined in groups wherein the feeding station positions a corresponding placement pattern of the objects to be sorted onto the belt conveyor which placement pattern accommodates all placing device groups. Depending on the required sorting output, with an adjustment based on the determined optimal placement pattern, by means of a sorting device, which has several feeding devices and several placing devices, the respectively preselected sorting specification can be performed optionally with only some of the manipulation devices that are available which are individually optimally used by being operated with the method according to the invention. The sorting device can be variably used by means of the method according to the invention for most different sorting tasks wherein it is only necessary to program the robots accordingly by means of the control unit; complex constructive retooling or retrofitting is not required.